The invention relates to fluid systems including hydraulic systems of the type wherein a reservoir supplies fluid to a hydraulic pump which supplies high pressure fluid to one or more hydraulic fluid operated devices. Such fluid operated devices include piston-cylinder assemblies and hydraulic motors or the like, as well as lubrication systems wherein a reservoir supplies a fluid to a pump which, in turn, supplies a lubricant to one or more bearings. Various other applications such as commercial processes utilizing various fluids will be apparent to those skilled in the art. The invention has application to systems utilizing (1) petroleum based lubricants and hydraulic fluids and (2) synthetic fluids including synthetic hydraulic fluids as well as to other fluids.
Many hydraulic systems in both industrial and commercial applications are exposed to substantial contamination and, thus, are highly vulnerable. For example, garbage trucks commonly have hydraulic system utilizing thirty gallon reservoirs and suffer repetitive failures of expensive hydraulic equipment. Similar problems occur in numerous other industrial hydraulic systems. Frequently the expense of the individual hydraulic system components is very great. In addition, the down time of the equipment involved is also very significant.
The reservoirs for typical fluid systems are typically open to the atmosphere. The exposure of the hydraulic fluid or the lubricant in the reservoir to the atmosphere is undesirable because it results in contamination of the lubricant or other hydraulic fluid as well as contamination of the atmosphere. The contamination of the hydraulic or other fluid is typically caused by the ambient air entering and leaving the reservoir during operation of the system. The interior metal surfaces of the reservoir are typically coated with a sticky oil to which dirt particles in the dirty ambient air attach themselves. This process of "air breathing", as it is called in industry, is a major source of hydraulic or other fluid contamination.
In addition there is another detrimental effect to the lubricant or hydraulic fluid. Moisture contamination may be even more damaging. The water vapor pressure of the ambient air varies with many environmental factors. Whenever the temperature of the reservoir is less than the dew point of the ambient air, condensation occurs. The condensed water then enters the hydraulic fluid system. Numerous problems can and do result from this effect. Adsorption of gases into the hydraulic fluid may also occur.
As a result of the dirt and moisture contamination of the hydraulic fluid, the lives of all moving parts in the hydraulic system including pumps and various moving apparatus are greatly reduced. In addition, hydraulic fluid and filter must be changed more frequently.
More specifically, in the conventional hydraulic system the quantity of fluid in the hydraulic system reservoir can vary substantially during the operating cycle. Various valves may be opened or closed, a cylinder may be full or empty, etc., and, thus the quantity of hydraulic fluid in the reservoir varies substantially during normal operation. In addition, the volumetric expansion rate for the hydraulic fluid and air in the reservoir differs substantially. In the conventional system the air breather cap, which may also be a fill cap, allows air to enter and leave as the volume of hydraulic fluid and air in the reservoir varies. For example, the oil level in the reservoir may change only 10 percent due to temperature changes and system operation. However, the air volume above the reservoir may vary 30 percent from temperature changes. This results in a 40 percent total volume change. Since the oil remains in the system, the entire 40 percent volume change is created by the air.
The prior art includes the apparatus described in U.S. Pat. Nos. 4,135,635; 3,330,902; 2,095,752; 1,652,793; and 4,161,964. These devices have not been wholly satisfactory because, in part, they expose a reservoir to high pressure or to a negative pressure, at least in come cases. Thus, if such prior art were retrofitted in some existing hydraulic systems, it is probable that damage to the reservoir might result. In addition, the prior art apparatus did not adequately provide for removal of moisture from the air within a closed hydraulic system.
It is an object of the invention to provide apparatus which eliminates contamination of the lubricant or other hydraulic fluid.
It is another object of the invention to provide apparatus which visually shows if the air within the system is dry or if it is wet, also helping to determine if the system has an air leak.
It is another object of the invention to provide apparatus which eliminates atmospheric contamination.
It is another object of this invention to provide apparatus which visually shows if the air within the system is at a slight positive or negative pressure.
It is another object of the invention to provide apparatus which will not require periodic maintenance.
It is another object of this invention to provide apparatus which increases surface area for the rejection of excess heat.
Yet another object of the invention is to provide apparatus which attains the various objects of the invention while being very inexpensive to manufacture and install even on existing hydraulic systems.
Still another ojbect of the invention is to provide apparatus which is simple to manufacture.